Children from low-income language minority backgrounds begin kindergarten at a significant disadvantage compared to their English-speaking peers, highlighting the need to provide them with enriching educational experiences in early childhood. Many state readiness standards now highlight preschool science as a key domain in the preparation of young children for the transition into formal schooling (Head Start, 2007). Yet, the lack of studies with rigorous research designs to evaluate the effectiveness of preschool science curricula has prevented researchers from drawing conclusions about best practices. In addition, preschool science curricula have been designed for classrooms made up of European American children from middle income backgrounds and the effectiveness of these programs have not been tested with low-income Latino preschool children from Spanish- speaking backgrounds. The overall goal of the proposed study is to design and test the efficacy of a preschool science curriculum for low-income Latino children that focuses on improving their conceptual understanding of germ contagion and contamination, and food and nutrition, an area of interest to NIH related to developing creative and innovate research education to deliver information about healthy living in science to children. Our study is novel in that it integrates health and biology concepts in a multi-unit science curriculum, instead of introducing health information as a stand-alone topic outside of science, typical of preschool programs. In the proposed research, 40 preschool classrooms will be assigned randomly to one of two experimental groups: 1) a treatment group that receives the biology-based health science curriculum; 2) an attention control group that receives a standard health curriculum from published, on-line materials. Within each experimental group, half of the classrooms will receive the curriculum in Spanish and the other half will receive the curriculum in English. All children, ages 4 and 5, will participate in pre- and postest assessment sessions. We expect that relative to control group, children will show an increase in conceptual understanding of health concepts related to biological process, and science inquiry skills as measured by their capacity to ask questions and generate explanations. There will be significant increases on measures of science understanding and inquiry skills for both groups of children (those receiving the instruction in Spanish and those in English) although the overall effects of the experimental curriculum will be stronger for children receiving the instruction in their primary language (Spanish).This study will provide vital information for the development and dissemination of a biology-based preschool health science program particularly for low-income Latino children from Spanish-speaking backgrounds, but appropriate for different types of learners.